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Technical Specifications



  • Width: 86.5 mm
  • Height: 86.5 mm
  • Depth: 22.8 mm
  • Weight: 140 g (incl. battery)
  • Casing material: PETG (3D printed)

User Interface

  • E-paper display
  • Six tactile buttons with LED illumination
  • Proximity detection (coming soon via software update)


  • Type: Single color E-paper (non-illuminated)
  • Size: 2.9"
  • Resolution: 296 x 128
  • Model number: Good Display GDEY029T94


  • 2.4Ghz WiFi
    • MQTT protocol (Supports MQTT Discovery)
  • USB Type-C connector
    • Charging
    • Firmware update (USB DFU mode)
    • Debug messages (USB CDC mode)


  • ESP32-S2
    • Xtensa® Single­Core 32­bit LX7
    • Integrated WiFi modem: IEEE 802.11 b/g/n (2.4 GHz Wi­Fi)
  • Supports OTA (Over-The-Air firmware update)
  • Native USB for firmware update and debug
  • Advanced security features

Environmental Sensor

  • Sensirion SHTC3 high accuracy Temperature and Relative Humidity sensor
  • Temperature accuracy: ±0.2°C (0°C to 60°C)
  • Humidity accuracy: ±2% RH (20% RH to 80% RH)


  • 3.7 V Lithium-Ion 18650 battery cell (non-protected) is required
  • WARNING: maximum cell length is 65.5 mm. Button top cells might not fit properly
  • Expected battery life: 18 months
    • Assuming Panasonic NCR18650B 3400mAh or equivalent
  • Battery safety features:
    • Reverse polarity protection
    • Over-discharge protection
    • Over-charge protection
    • Overload protection

Charging at extreme temperatures (below 0°C or above 50°C) is not recommended. Check your battery specifications for more information


  • Any standard USB Type-C power supply is sufficient for charging

    Can also be charged using any computer USB port

  • Battery charging current: 780 mA

    Make sure the selected battery can be safely charged at this rate

  • Expected recharging time from empty: 4 hours

    Assuming Panasonic NCR18650B 3400 mAh or equivalent